Tiny Tuner is all but worthless, in my opinion. The reason why you don't see the Cat Diagnostic check in Tiny Tuner for your 04 file is because it probably wasn't added for your specific 04 PCM's OS. So you will either need to add it yourself (and know how to do that and where it is in your particular OS), or find someone who knows where it is in the 04 OS you are using and have them add it to Tiny Tuner and then have them send you the updated Tiny Tuner definition file. Have fun with that. I've been told by people who actually write tuning software for a living that GM V6 applications have litterally hundreds of different OS's (operating systems). So just because someone found out where it was in 1 particular OS doesn't mean that can be applied to other OS's, not even for the same model year car with the same engine (because there were so many different OS's used).

07 applications SHOULD also have this diagnostic. I don't see why GM would have added it and then later removed it. I know in HP Tuners you have the option of disabling both the CAT and post-cat O2 diagnostics in SOME 2004-newer applications; but I think this is only applicable to the newer style CAN bus type PCMs and ECMs. Unfortunately, HP Tuners doesn't support any 2006-newer 3800 applications at all (and I doubt that will ever change).